An Experiment on Unsteady Flow Over an Oscillating Airfoil

In order to enhance understanding of viscous-dominated blade flutter and to provide experimental data for validating unsteady viscous flow solutions, unsteady flow over a 2-D NACA-65 airfoil oscillating in torsion at an amplitude of 2° and a reduced frequency up to 0.69 has been experimentally investigated in a low-speed wind tunnel under different loading conditions. Unsteady pressure distribution is measured on both suction and pressure surfaces using pressure transducers. On the suction surface hot-film measurements are conducted to indicate the development of the unsteady boundary layer. Unsteady boundary layer behaviour and its effects on the airfoil’s aeroelasticity at the different loading conditions are demonstrated. The results also throw some light on understanding the onset mechanism of “dynamic stall” which involves a persistent convective pressure wave pattern with marked unstable aeroelastic characteristics.

Download Full-text

Effect of Reduced Frequency on the Boundary Layer of a Plunging Airfoil

ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 1 ◽

10.1115/esda2010-24574 ◽

2010 ◽

Author(s):

F. Rasi Marzabadi ◽

M. R. Soltani ◽

M. Masdari

Keyword(s):

Boundary Layer ◽

Separation Bubble ◽

Reynolds Numbers ◽

Boundary Layer Transition ◽

Unsteady Boundary Layer ◽

Layer Transition ◽

Laminar Separation ◽

Pressure Transducers ◽

Reduced Frequency ◽

Hot Film

This investigation addresses the boundary layer study of a plunging airfoil. It specifically concerns the effect of reduced frequency on transition and separation/reattachment of the unsteady boundary layer. The wind tunnel measurements were conducted using multiple hot-film sensors, pressure transducers and a boundary-layer rake, at Reynolds numbers of 0.42 to 0.84 million, and over reduced frequencies from 0.05 to 0.11. It was observed the boundary layer transition occurs by a laminar separation bubble. The unsteady laminar separation is promoted (delayed) by the increase of the reduced frequency in upstroke (downstroke) portion of the equivalent angle of attack.

Download Full-text

Measurement of Unsteady Flow and Heat Transfer in a Linear Turbine Cascade

Volume 1: Turbomachinery ◽

10.1115/92-gt-323 ◽

1992 ◽

Cited By ~ 11

Author(s):

X. Liu ◽

W. Rodi

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Unsteady Flow ◽

Boundary Layers ◽

Suction Side ◽

Turbine Cascade ◽

Transfer Coefficients ◽

Flow And Heat Transfer ◽

Background Turbulence ◽

Hot Film

A detailed experimental study has been conducted on the wake-induced unsteady flow and heat transfer in a linear turbine cascade. The unsteady wakes with passing frequencies in the range zero to 240 Hz were generated by moving cylinders on a squirrel cage device. The velocity fields in the blade-to-blade flow and in the boundary layers were measured with hot-wire anemometers, the surface pressures with a pressure transducer and the heat transfer coefficients with a glue-on hot film. The results were obtained in ensemble-averaged form so that periodic unsteady processes can be studied. Of particular interest was the transition of the boundary layer. The boundary layer remained laminar on the pressure side in all cases and in the case without wakes also on the suction side. On the latter, the wakes generated by the moving cylinders caused transition, and the beginning of transition moves forward as the cylinder-passing frequency increases. Unlike in the flat-plate study of Liu and Rodi (1991a) the instantaneous boundary layer state does not respond to the passing wakes and therefore does not vary with time. The heat transfer increases under increasing cylinder-passing frequency even in the regions with laminar boundary layers due to the increased background turbulence.

Download Full-text

Boundary Layer Development in the BR710 and BR715 LP Turbines—The Implementation of High-Lift and Ultra-High-Lift Concepts

Journal of Turbomachinery ◽

10.1115/1.1457455 ◽

2002 ◽

Vol 124 (3) ◽

pp. 385-392 ◽

Cited By ~ 43

Author(s):

R. J. Howell ◽

H. P. Hodson ◽

V. Schulte ◽

R. D. Stieger ◽

Heinz-Peter Schiffer ◽

...

Keyword(s):

Boundary Layer ◽

Test Facility ◽

Surface Boundary ◽

Unsteady Boundary Layer ◽

Suction Surface ◽

High Lift ◽

Surface Boundary Layer ◽

Cold Flow ◽

Layer Behavior ◽

Lp Turbine

This paper describes a detailed study into the unsteady boundary layer behavior in two high-lift and one ultra-high-lift Rolls-Royce Deutschland LP turbines. The objectives of the paper are to show that high-lift and ultra-high-lift concepts have been successfully incorporated into the design of these new LP turbine profiles. Measurements from surface mounted hot film sensors were made in full size, cold flow test rigs at the altitude test facility at Stuttgart University. The LP turbine blade profiles are thought to be state of the art in terms of their lift and design philosophy. The two high-lift profiles represent slightly different styles of velocity distribution. The first high-lift profile comes from a two-stage LP turbine (the BR710 cold-flow, high-lift demonstrator rig). The second high-lift profile tested is from a three-stage machine (the BR715 LPT rig). The ultra-high-lift profile measurements come from a redesign of the BR715 LP turbine: this is designated the BR715UHL LP turbine. This ultra-high-lift profile represents a 12 percent reduction in blade numbers compared to the original BR715 turbine. The results from NGV2 on all of the turbines show “classical” unsteady boundary layer behavior. The measurements from NGV3 (of both the BR715 and BR715UHL turbines) are more complicated, but can still be broken down into classical regions of wake-induced transition, natural transition and calming. The wakes from both upstream rotors and NGVs interact in a complicated manner, affecting the suction surface boundary layer of NGV3. This has important implications for the prediction of the flows on blade rows in multistage environments.

Download Full-text

Application of hot-film anemometry to resolve the unsteady boundary layer transition of a laminar airfoil experiencing limit cycle oscillations

Experiments in Fluids ◽

10.1007/s00348-020-2907-y ◽

2020 ◽

Vol 61 (2) ◽

Cited By ~ 1

Author(s):

Marc Braune ◽

Stefan Koch

Keyword(s):

Boundary Layer ◽

Limit Cycle ◽

Boundary Layer Transition ◽

Limit Cycle Oscillations ◽

Unsteady Boundary Layer ◽

Layer Transition ◽

Hot Film ◽

Hot Film Anemometry

Download Full-text

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

Journal of Turbomachinery ◽

10.1115/1.1791646 ◽

2004 ◽

Vol 126 (4) ◽

pp. 663-676 ◽

Cited By ~ 16

Author(s):

M. T. Schobeiri ◽

B. O¨ztu¨rk

Keyword(s):

Boundary Layer ◽

Separation Bubble ◽

Wake Flow ◽

Suction Surface ◽

Low Pressure Turbine ◽

Reduced Frequency ◽

Boundary Layer Development ◽

Unsteady Wake ◽

Unsteady Wake Flow ◽

Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and reattachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Download Full-text

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Re-Attachment Along the Surface of a Low Pressure Turbine Blade

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-53929 ◽

2004 ◽

Cited By ~ 5

Author(s):

M. T. Schobeiri ◽

B. O¨ztu¨rk

Keyword(s):

Boundary Layer ◽

Separation Bubble ◽

Wake Flow ◽

Suction Surface ◽

Low Pressure Turbine ◽

Reduced Frequency ◽

Boundary Layer Development ◽

Unsteady Wake ◽

Unsteady Wake Flow ◽

Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Download Full-text

Effect of amplitude and mean angle-of-attack on the boundary layer of an oscillating aerofoil

The Aeronautical Journal ◽

10.1017/s0001924000002670 ◽

2008 ◽

Vol 112 (1138) ◽

pp. 705-713 ◽

Cited By ~ 4

Author(s):

M. R. Soltani ◽

A. Bakhshalipour

Keyword(s):

Boundary Layer ◽

Transition Point ◽

Angle Of Attack ◽

Wind Tunnel Test ◽

Leading Edge ◽

Stream Velocity ◽

Velocity Amplitude ◽

Surface Pressure Distribution ◽

Reduced Frequency ◽

Hot Film

Abstract Extensive experiments were conducted to study the effect of various parameters on the surface pressure distribution and transition point of an aerofoil section used in a wind turbine blade. In this paper details of the variation of transition point on the aforementioned aerofoil are presented. The aerofoil spanned the wind-tunnel test section and was oscillated sinusoidally in pitch about the quarter chord. The imposed variables of the experiments were free stream velocity, amplitude of motion, mean angle-of-attack, and oscillation frequency. The spatial-temporal progressions of the leading-edge transition point and the state of the unsteady boundary-layer were measured using eight closely-spaced, hot-film sensors (HFS). The measurements show that: (i) Reduced frequency has a pronounced effect on the variations of the transition point. (ii) There exists a hysteresis loop in the dynamic transition location and its shape varies with the reduced frequency and mean angle-of-attack.

Download Full-text

Intermittent Behavior of the Separated Boundary Layer Along the Suction Surface of a Low Pressure Turbine Blade Under Periodic Unsteady Flow Conditions

Volume 3: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68603 ◽

2005 ◽

Cited By ~ 4

Author(s):

B. O¨ztu¨rk ◽

M. T. Schobeiri ◽

David E. Ashpis

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Turbine Blade ◽

Low Pressure ◽

Boundary Layer Transition ◽

Wake Flow ◽

Unsteady Boundary Layer ◽

Flow Conditions ◽

Suction Surface ◽

Low Pressure Turbine

The paper experimentally and theoretically studies the effects of periodic unsteady wake flow and aerodynamic characteristics on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experiments were carried out at Reynolds number of 110,000 (based on suction surface length and exit velocity). For one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, intermittency behavior were experimentally and theoretically investigated. The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed in previously to the LPT cases, where separation occurs on the suction surface at a low Reynolds number. The results of the unsteady boundary layer measurements and the intermittency analysis were presented in the ensemble-averaged, and contour plot forms. The analysis of the boundary layer experimental data with the flow separation, confirms the universal character of the relative intermittency function which is described by a Gausssian function.

Download Full-text